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Should the solar backup heater stay warm all day?
How do you decide whether a solar water-heating system’s conventional backup should maintain its setpoint continuously or heat only when solar storage can’t meet demand? I can see the appeal of having hot water ready through a cloudy stretch, but I’m also curious whether keeping the backup on all day uses more energy than heating only as needed.
I imagine the answer depends partly on where the backup sits. Is it an auxiliary element in the solar storage tank, or a separate heater downstream? How does that layout affect comfort during a cloudy day or a busy morning, and are there control arrangements that make one strategy impractical? I’d also want to know what the system manual or installer recommends before changing any settings.
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I’d lean toward backup that comes on when the solar store can’t meet demand, rather than maintaining its setpoint all day: I’d trade a little less immediate readiness for avoiding backup heating when solar has already done the work. If a cloudy spell or slow recovery makes that inconvenient, I’d favor a control with a reliable demand trigger - but only if the system manual or installer confirms that operating mode suits the particular layout.
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